Electrostatographic reproduction machines

ABSTRACT

An electrostatographic reproduction machine having a web cassette comprised of separable portions for feeding a web between the photoreceptive surface and the developer means of the machine to provide a developed image on the web for subsequent transfer to suitable support material.

United States Patent [191 Cook [ ELECTROSTATOGRAPHIC REPRODUCTION MACHINES [75] Inventor: John Hayward Cook,

Fawbridgeworth, England [73] Assignee: Xerox Corporation, Stamford,

Conn.

[22] Filed: Mar. 11, 1974 [211 App]. No.: 450,267

[52] US. Cl. 355/3 R; 355/16 [51] Int. Cl. 603G 15/00 [58] Field of 355/3, 16; 354/214 [56] References Cited UNITED STATES PATENTS 2,504,527 4/1950 Huebner 354/214 51 Dec. 23, 1975 3,432,231 3/1969 Gardner 355/8 3.617.124 11/1971 Haugen 355/16 3,820,985 6/1974 Gaynor 355/3 Primary Examiner-John M. Horan ABSTRACT An electrostatographic reproduction machine having a web cassette comprised of separable portions for feeding a web between the photoreceptive surface and the developer means of the machine to provide a developed image on the web for subsequent transfer to suitable support material. 7

19 Claims, 12 Drawing Figures US. Patent Dec. 23, 1975 Sheet 1 of6 3,927,934

U.S. Patent Dec. 23, 1975 Sheet 2 of6 3,927,934

FIG. 2

US. Patent Dec. 23, 1975 Sheet 3 of6 3,927,934

US. Patent Dec. 23, 1975 Sheet 4 of6 3,927,934

US Patent Dec. 23, 1975 Sheet 5 of6 3,927,934

US. Patent Dec. 23, 1975 Sheet 6 of 6 3,927,934

ELECTROSTATOGRAPHIC REPRODUCTION MACHINES The present invention relates to an electrostatographic reproduction machine.

In this specification, the expression electrostatographic reproduction machine refers to a machine for producing one or more prints or copies from at least one electrostatic latent image. The expression electrostatographic member" refers to a member for producing and utilising an electrostatic latent image.

The production of an electrostatic latent image may be carried out in various ways, as is well known. The basic and most conventional electrostatographic process or method is taught by C. F. Carlson in U.S. Pat. No. 2,297,691. This method involves producing a uniform electrostatic charge on a photoconductive insulating layer. in practice, it is possible for the insulating layer to have a protective overlayer or other overlayer known in the art of xerography. The charged layer is exposed to imaging radiation (especially light) to discharge selectively the photoconductive layer to form the electrostatic latent image. The latent image may then be developed in any known way. Examples of known development methods are cascade development" disclosed in U.S. Pat. No. 2,618,552; powder cloud development disclosed in U.S. Pat. No. 2,221,776; and magnetic brush development disclosed for instance in U.S. Pat. No. 2,874,063. Another example of a known development method is a liquid development method described by R. W. Gundlach in U.S. Pat. No. 3,084,043. In this method, development is carried out with a polar liquid developer. Such a developer is stable, i.e., it will respond to an electrostatic field as a homogeneous unit without separation of the components of the liquid developer. As described in U.S. Pat. No. 3,084,043, the polar liquid developer is applied by a rotatable member having a plurality of raised portions defining a substantially regular patterned surface and a plurality of portions depressed or sunken below the raised portions. The liquid developer is present in the depressed portions and is doctored by a doctor blade.

The present invention provides an electrostatographic reproduction machine in which a web is interposed between an electrostatographic member and developer means such that said web is feedable between first and second separable parts of a sectional cassette for said web.

According to one aspect of the present invention, there is provided an electrostatographic reproduction machine comprising an electrostatographic member and developer means arranged relative to each other for allowing a web to be interposed between said electrostatographic member and said developer means such that said web is feedable between first and second separable parts of a sectional cassette for said web.

According to another aspect of the invention, there is provided a sectional cassette suitable for use in an electrostatographic reproduction machine of the present invention, said cassette comprising first and second separable parts each for holding a corresponding portion of a web to be interposed between said electrostatographic member and said developer means such that said web will be feedable between said first and second separable parts of the cassette.

Preferably, the electrostatographic member is movable from an operative position to an inoperative position in which said web is insertable into said machine and such that said web will be interposed between said electrostatographic member and said developer means when said electrostatographic member is returned to said operative position. Conveniently, when the electrostatographic member is in said inoperative position, the cassette is insertable into said machine with said parts of the cassette in mutual engagement and thereafter said parts are separable to allow said electrostatographic member to be returned to said operative position. The motion of the electrostatographic member between its operative and inoperative positions may be provided by the electrostatographic member being pivotable between these positions. Preferably, for this purpose, the electrostatographic member is mounted on at least one pivotable link, which may have any suitable shape.

Preferably, the electrostatographic member is in the configuration of a rotatable drum. However, the electrostatographic member could have any other suitable configuration, for example the configuration of a belt. In the case of the electrostatographic member having the configuration of a rotatable drum, preferably the electrostatographic member and the developer means are arranged to allow said web to conform with said drum configuration in an are of web that subtends an angle greater than 180 relative to the axis of rotation of said electrostatographic member.

The developer means may be any suitable developer means known as such for developing an electrostatic latent image. The present invention finds particular application to the case where the developer means is adapted for applying developer to said interposed web to provide on said web developer image conforming to an electrostatic latent image provided by said electrostatographic member. Examples of developer means for this purpose are developer means adapted for cascade development, powder cloud development, magnetic brush development, or liquid development. Preferably, the developer image is transferable to support material. The transferred developer image can be fixed or become permanently fixed to the support material. In the case of a liquid developer system, a heat fusing device is not necessary to fix the transferred developer image to the support material, compared with developer systems using such heat fusing devices for fusing toner powder images.

Preferably, a developer means for applying liquid developer comprises a rotatable roll for applying liquid developer to said web, said roll comprising a plurality of spaced apart solid parts defining a substantially regular surface, said solid portions being separated by recesses for receiving liquid developer for said application. However, it should be noted that other developer means could be used for applying liquid developer, for example a belt.

Preferably, when a developer image is to be trans- Preferably, the machine of the present invention comprises support means for a said part of the cassette, said support means being adapted for moving this part of the cassette in a predetermined path out of or into engagement with said other part of the cassette. For this purpose, said support means is preferably pivotable, such as when said support means comprises at least one pivotable link for mounting a said part of the cassette. Preferably, the machine comprises static support means for the other said part of the cassette.

In the cassette of the present invention, preferably said first and second separable parts of the cassette are adapted to remain in mutual engagement until deliberately separated. For example, one said part of the cassette may have a recess, and the other said part of the cassette may have a tongue for entering said recess. Alternatively or additionally, the cassette may have latch means for releasably holding said parts of the cassette together. If desired, the cassette may have a window to allow material of said web inside the cassette to be inspected. Conveniently, said separable parts of the cassette may have profiled openings to lead web material out of said separable parts in a path that will facilitate said feeding of the web. The web may have any suitable composition. Preferably, the web is a web of polymeric material, conveniently a polyethylene web.

The present invention will now be described by way of example with reference to the accompanying drawings, in which identical reference numerals refer to corresponding items.

FIG. 1 shows schematically one electrostatographic reproduction machine in accordance with the present invention.

FIG. 2 shows schematically another electrostatographic machine in accordance with the present invention.

FIG. 3 shows a sectional cassette suitable for use in the reproduction machine of FIG. 1 or 2.

FIGS. 4 to 11 illustrate the sequence of operations for removing or replacing a cassette in the reproduction machine of FIG. 2.

FIG. 12 shows schematically a gravure roll for applying liquid developer material in the reproduction machine of FIG. 1 or 2.

In FIG. 1, the reproduction machine is a xerographic reproduction machine comprising a xerographic member in the configuration of a rotatable drum generally designated 1. The drum 1 has a photoconductive layer 2, which may be any photoconductive layer known for xerography. For instance, the layer 2 may be a layer of amorphous selenium or a resin binder layer in which a photoconductive organic material is dispersed. The layer 2 may have a protective overlayer or any other overlayer known for xerographic drums. The drum 1 is detechably mounted between and by the terminal portions of two opposed pivotable links 3 that are rigid relative to each other. Only one of the links 3 is shown in FIG. 1 because the links 3 are identical. The inner limits of the pivotable motions of the links 3 represent the operative location of drum 1.

A web 4 of any suitable permittivity (e.g. a web of polymeric material, especially a polyethylene web) is advanceable from a supply chamber 5 downwards, then around a substantial portion of the periphery of the drum 1, and finally upwards to a take-up chamber 6. The web 4 can be advanced while the drum 1 is rotating or stationary. Correct tracking of the web 4 around the drum 1 is facilitated by the web 4 passing over position adjustable guide rolls 7, 8. If desired, the web 4 may have sprocket holes in either or both of its marginal areas, in order to facilitate controlled advancing of the web 4. In this case, at least one of the guide rolls 7, 8 will have complementary projections for engaging the sprocket holes. Although not shown, the machine may incorporate sensor means for detecting loss of tension in the web 4, especially as would result from a break in the web. The sensor means preferably react to the web breaking by putting the machine into a close down mode, in which the tail ends of the broken web are drawn into the chambers 5, 6.

The chambers 5, 6 each have an open side 9 or 10 respectively, as shown in FIG. 3, thereby allowing communication between these chambers in the closed configuration of the sectional cassette represented by the chambers 5, 6. Chamber 5 is detachably mounted at a static location. For this purpose, chamber 5 has a central rotatable bushing 11 through which a removable spindle 12 passes. The ends of the spindle 12 project beyond the sides of the cassette, and may be detachably mounted in or supported by suitable bearings (not shown) in the framework of the machine. This mounting or supporting is at locations spaced between and from the links 3. Chamber 6 is detachably mounted between and by the terminal portions of two opposed pivotable links 13 that are rigid relative to each other. Only one of the links 13 is shown in FIG. 1 because the links 13 are identical. For the detachable mounting of chamber 6, a spindle 14 passes removably through a central rotatable bushing 15 in chamber 6. The ends of the spindle 14 are received in notches or guideways 16 in the tops of links 13. The limits of the pivotable motions of links 13 respectively correspond to open and closed configurations for the sectional cassette 5, 6.

As shown in FIG. 1, the cassette 5, 6 has an open configuration when the drum 1 is at its operative location. However, as shown in FIG. 2, the cassette 5, 6 may be in closed configuration when the drum 1 is at its operative location. In the embodiment shown in FIG. 2, the web 4 in the cooperating chambers 5, 6 will be practically isolated from the general interior of the machine. However, it is not essential for the closed cassette to conceal the web wholly. For example, as shown in FIG. 3, chamber 5 could have a radial window 16 to allow the web to be inspected. For the closed configuration of the cassette 5, 6, the chambers may be adapted to stay together until deliberately separated. For example, as shown in FIG. 3, this could be done by chamber 5 having a recess 17 in the rim defining its open side 9, and chamber 6 having a tongue 18 in the rim defining its open side 10. Alternatively or additionally, chambers 5, 6 could be provided with latch means 19 for releasably holding said chambers together, e.g. a spring biased ball or other detent provided on one chamber for entering a recess provided on the other chamber.

The motions of the pivotable links 3 and 13 impose a corresponding sequence of operations on the installing or removing of a cassete 5, 6. In carryingout these operations, a hinged cover 22'of the machine is first lifted or opened to allow pivoting of the links 3 and 13. For FIG. 1, the sequence of operations requires guide rolls 7, 8 to be repositioned, and then the drum 1 to be swung by links 3 into its inoperative location. This permits the links 13 to be pivoted to swing cassette chamber 6 into closed configuration with chamber 5.

The chambers and 6 may then be locked together by latch means 19. Any slack in the web 4 corresponding to the last portion of the web 4 to embrace the drum 1 in its operative location may then be taken up. If desired, the last portion of the web 4 to embrace the drum 1 could be a trailer portion that is not exposed in the machine. This will ensure that during the removing of the cassette there will be no portion of exposed web outside the cassette which could be touched by the person removing the cassette. The cassette may be replaced by a further cassette 5, 6 enclosing a fresh web 4. By reversing the sequency of operations indicated above, the fresh web 4 will be located appropriately around the drum 1 in its operative location. If desired, the first portion of the web 4 to embrace the drum 1 could be a leader portion that is not exposed in the machine.

The sequence of operations contemplated by FIGS. 2 and 4 to 11 requires the cassette 5, 6 to be in closed configuration when the drum 1 is in its operative location see FIG. 2. For removing or replacing the cassette 5, 6, the chambers 5 and 6 are separated (see FIG. 4) and the guide rolls 7, 8 repositioned. In doing this, chamber 6 is swung away by pivoting the links 13 See FIG. 4. Then the drum 1 is swung by links 3 into its inoperative location see FIG. 5. After this, links 13 are pivoted to swing chamber 6 back into closed configuration with chamber 5 see FIG. 6. Chambers 5 and 6 are then latched together by latch means 19. Any slack in the web 4 corresponding to the last portion of the web 4 to embrace the drum 1 in its operative location is taken up. If desired, the last portion of the web 4 to embrace the drum 1 could be a trailer portion that is not exposed in the machine. This will ensure that during the removing of the cassette there will be no portion of exposed web outside the cassette which could be touched by the person removing the cassette. The cassette may then be replaced by a further cassette 5, 6 enclosing a fresh web 4. If desired, the first portion of the web 4 to embrace the drum 1 could be a leader portion that is not exposed in the machine. By reversing the sequence of operations just described, the fresh web 4 will be located appropriately around the drum 1 in its operative location see FIGS. 9 to 11.

In FIG. 1, when the drum 1 is in its operative location, the drum 1 will have process stations A to E spaced apart around drum 1. These stations are adapted to be operated in sequence with corresponding rotations of the drum 1, as indicated in the following description of FIG. 1.

Process station A is adjacent a portion of the exterior of the drum 1 not embraced by the web 4. Process station A is a charging station having a corona discharge device for depositing a uniform electrostatic charge on the photoconductive layer of the drum 1. The corona discharge device may be one known for xerography. During the charging by station A, the pho toconductive layer 2 will rotate preferably once past station A. The web 4 will preferably remain at rest during this rotation.

After station A in the path of motion of the drum 1 in FIG. 1, there is a process station B adjacent another portion of drum 1 not embraced by the web 4. This station is an exposure station comprising a suitable scanning system. The scanning system may be one known for xerography. Station B will project a light imaging pattern onto the photoconductive layer 2, preferably during one rotation of drum 1. The imaging 6 pattern corresponds to an original comprised by a document fed through station B by feed rolls 23, 24, 25, 26. The imaging pattern selectively dissipates the charge on the photoconductive layer 2, thereby producing on this layer an electrostatic latent image corresponding to the original.

After station B in the path of motion of the drum 1 is process station C adjacent a portion of drum 1 embraced by the web 4. This station is a developer station comprising a rotatable roll 30. This roll is a gravure roll having a plurality of spaced apart peripheral solid portions (i.e., lands" 31, defining a substantially regular surface. see FIG. 12. These solid portions are separated by recesses (i.e., valleys") 32 for receiving polar liquid developer. The solid portions 31 may be interconnected to give a helical thread extending along the roll 30. The roll 30 is mounted in a developer sump 33. A rotatable roll 34 is present in the sump 33 for dipping into polar liquid developer. The roll 34 has a generally smooth surface. During rotation of the roll 34, this roll will apply polar liquid developer to the recesses 32. A doctor blade 35 serves to wipe excess liquid developer from the solid portions 31 of the roll 30 Preferably, the doctor blade will penetrate partly into the recesses 32, to ensure that the outer level of liquid developer present in these recesses will be below the tops of the solid portions or lands 31 before this developer is applied to the web 4. During operation of station B, the photoconductive layer 2 and the web 4 will move together past station C, such that the electrostatic latent image will attract to the web 4 polar liquid developer from the recesses or valleys 32 of the roll 30. In this way, a transferable developer image is formed on the web 4. This image corresponds to the latent image. The speeds of rotation of the rolls 30 and 34 will be appropriate to the functions described above for them.

After station C in the path of motion of the drum 1 is process station D adjacent another portion of the drum 1 embraced by the web 4. This station is a transfer station for transferring the developer image from web 4 to a paper sheet 41 delivered from a stack 42 of paper sheets. The sheets may be delivered from this stack by any suitable sheet feeding mechanism known for xerography. For example, a friction roll 43 will advance the uppermost sheet of the stack 42 into the nip between a stand friction drive rolls 44, 45, which then pass the sheet to the web 4. Suitable control means (not shown) may be present in the sheet feeding mechanism to prevent premature feeding of sheets from the stack 42. Station D also comprises a rotatable pressure transfer roll 46 for pressing the delivered sheet 41 against the transferable developer image on the web 4, such that developer material is absorbed in image configuration by said sheet. The leading edge of the sheet 41 may be separated in any convenient way from the web 4. However, preferably this is done by advancing the web 4 around a sufficiently small diameter static roll or rod 47, to allow the beam strength of the sheet 41 to cause the leading edge of the advancing sheet 41 to separate from the advancing web 4. The sheet 41 then passes down a delivery ramp or tray 48. The transferred image on the sheet 41 does not require any specific fixing treatment in view of absorption of developer material by this sheet. However, the sheet could be subjected to a gentle air flow to remove or reduce the content of any volatiles present in developer material on the sheet.

After station D in the path of motion of the drum 1 is process station E adjacent a portion of the drum 1 not embraced by the web 4. This station is an illumination station having a lamp for flooding with light the photo conductive layer 2. The flooding with light will destroy the latent image, and may be done after one copy has been made. However, it should be noted that multiple copies could be obtained from one latent image by redeveloping a residual developer image remaining on the web 4. This is a convenient way of operating the machine to obtain multiple copies.

It will be noted that the reproduction machine does not comprise a cleaning station for removing residual developer material from the drum 1. This is because web 4 prevents the polar liquid developer from contacting drum 1.

In FIG. 2, the reproduction machine has a different and simplified configuration compared with the machine of FIG. 1. Items that are functionally similar in FIGS. 1 and 2 have identical reference numerals. Therefore, FIG. 2 will now only be specifically described insofar as it is significantly different from FIG. 1. Compared with FIG. 1, it will be readily seen that the configuration of the machine of FIG. 2 provides a laterally disposed optical path instead of a vertical optical path as shown in FIG. 1. Furthermore, in FIG. 2, an illumination station EE is used instead of process station E of FIG. 1. Station EE comprises an electroluminescent strip for flooding with light the photoconductive layer 2 to destroy the latent image.

If desired, the machines of FIGS. 1 and 2 and their cassettes may be modified or varied according the the required circumstances. For example, the extent to which the interposed portion of the web 4 will conform to the exterior of the drum 1 will be such that the limiting ends of the arc of web 4 conforming to the exterior of the drum 1 will subtend any suitable angle relative to the axis of rotation of the drum 1. Conveniently, this angle will be greater than 180, for example as indicated by the machine configurations shown in FIGS. 1 and 2. If desired, the material of the cassette 5, 6 may be of metal, but preferably the cassette is formed from any suitable plastics material. If desired, where the web 4 passes out of chambers 5, 6, these chambers may have suitably profiled openings that will lead web material out of chambers 5, 6 in a path that will facilitate advancing of the web 4. Such profiled openings are shown in FIG. 3 as having outwardly directed curved lips 20, 21.

The present invention also comprises modifications and variations within the scope of the following claims.

What we claim is:

I. An electrostatographic reproduction machine comprising:

a photoconductive member;

developer means arranged relative to said photoconductive member;

web means interposed between said photoconductive member and said developer means; and,

a sectional cassette having first and second portions movable relative to each other for supporting said web therein, said web being feedable from one of said cassette portions to the other of said cassette portions between said photoconductive member and said developer means, said photoconductive member being movable from an operative position to an inoperative position in which said web is insertable into said machine, said web being interposed between said photoconductive member and said developer means when said photoconductive member is returned to said operative position.

2. The machine of claim 1, in which in said inoperative position of said photoconductive member, said cassette is insertable into said machine with said portions of the cassette in mutual engagement and thereafter said portions are separable to allow said photoconductive member to be returned to said operative position.

3. The machine of claim 2, in which said photoconductive member is pivotable between said operative and inoperative positions.

4. The machine of claim 3, in which said photoconductive member is mounted on at least one pivotable link.

5. The machine claim 4, in which said photoconductive member is in the configuration of a rotatable drum.

6. The machine of claim 5, in which said photoconductive member and said developer means are arranged to allow said web to conform with said drum configuration in an arc of web that subtends an angle greater than relative to the axis of rotation of said photoconductive member.

7. The machine of claim 6, in which said developer means is adapted for applying developer to said interposed web to provide on said web a developer image conforming to an electrostatic latent image provided on said photoconductive member.

8. The machine of claim 7, in which said developer means is adapted for applying liquid developer to said interposed web to provide said developer image.

9. The machine of claim 8, in which said developer means comprises a rotatable roll for applying liquid developer to said web, said roll comprising a plurality of spaced apart solid parts defining a substantially re gular surface, said solid portions being separated by recesses for receiving liquid developer for said application.

10. The machine of claim 9, comprising a rotatable pressure roll for pressing support material against said developer image such that this image will be urged to transfer to said support material.

11. The machine of claim 10, comprising guide means for changing the direction of motion of said web such that the beam strength of said support material will cause said support material to separate from said web.

12. An electrostatographic reproduction machine comprising:

a photoconductive member;

developer means arranged relative to said photoconductive member;

web means interposed between said photoconductive member and said developer means;

a sectional cassette having first and second portions movable relative to each other for supporting said web therein, said web being feedable from one of said cassette portions to the other of said cassette portions between said photoconductive member and said developer means; and,

support means for said first portion of the cassette, said support means being adapted for moving said first portion of the cassette in a predetermined path out of or into engagement with said second portion of the cassette.

13. The machine of claim 12, in which said support means is pivotable.

LII

17. The machine of claim 16, in which one of said portions of the cassette has a recess, and the other of said portions of the cassette has a tongue for entering said recess.

18. The machine of claim 17, in which said cassette has latch means for releasably holding said parts of the cassette together.

19. The machine of claim 18, in which said cassette has a window to allow material of said web inside the cassette to be inspected. 

1. An electrostatographic reproduction machine comprising: a photoconductive member; developer means arranged relative to said photoconductive member; web means interposed between said photoconductive member and said developer means; and, a sectional cassette having first and second portions movable relative to each other for supporting said web therein, said web being feedable from one of said cassette portions to the other of said cassette portions between said photoconductive member and said developer means, said photoconductive member being movable from an operative position to an inoperative position in which said web is insertable into said machine, said web being interposed between said photoconductive member and said developer means when said photoconductive member is returned to said operative position.
 2. The machine of claim 1, in which in said inoperative position of said photoconductive member, said cassette is insertable into said machine with said portions of the cassette in mutual engagement and thereafter said portions are separable to allow said photoconductive member to be returned to said operative position.
 3. The machine of claim 2, in which said photoconductive member is pivotable between said operative and inoperative positions.
 4. The machine of claim 3, in which said photoconductive member is mounted on at least one pivotable link.
 5. The machine claim 4, in which said photoconductive member is in the configuration of a rotatable drum.
 6. The machine of claim 5, in which said photoconductive member and said developer means are arranged to allow said web to conform with said drum configuration in an arc of web that subtends an angle greater than 180* relative to the axis of rotation of said photoconductive member.
 7. The machine of claim 6, in which said developer means is adapted for applying developer to said interposed web to provide on said web a developer image conforming to an electrostatic latent image provided on said photoconductive member.
 8. The machine of claim 7, in which said developer means is adapted for applying liquid developer to said interposed web to provide said developer image.
 9. The machine of claim 8, in which said developer means comprises a rotatable roll for applying liquid developer to said web, said roll comprising a plurality of spaced apart solid parts defining a substantially regular surface, said solid portions being separated by recesses for receiving liquid developer for said application.
 10. The machine of claim 9, comprising a rotatable pressure roll for pressing support material against said developer image such that this image will be urged to transfer to said support material.
 11. The machine of claim 10, comprising guide means for changing the direction of motion of said web such that the beam strength of said support material will cause said support material to separate from said web.
 12. An electrostatographic reproduction machine comprising: a photoconductive member; developer means arranged relative to said photoconductive member; web means interposed between said photoconductive member and said developer means; a sectional cassette having first and second portions movable relative to each other for supporting said web therein, said web being feedable from one of said cassette portions to the other of said cassette portions between said photoconductive member and said develOper means; and, support means for said first portion of the cassette, said support means being adapted for moving said first portion of the cassette in a predetermined path out of or into engagement with said second portion of the cassette.
 13. The machine of claim 12, in which said support means is pivotable.
 14. The machine of claim 13, in which said support means comprises at least one pivotable link for mounting said first portion of the cassette.
 15. The machine of claim 14, comprising static support means for said second portion of the cassette.
 16. The machine of claim 15, in which said first and second separable portions of the cassette are adapted to remain in mutual engagement until deliberately separated.
 17. The machine of claim 16, in which one of said portions of the cassette has a recess, and the other of said portions of the cassette has a tongue for entering said recess.
 18. The machine of claim 17, in which said cassette has latch means for releasably holding said parts of the cassette together.
 19. The machine of claim 18, in which said cassette has a window to allow material of said web inside the cassette to be inspected. 